 |
 |
Dear Andre, The voxel count within the volume sounds reasonable for a whole-brain analysis (minus possibly the most dorsal or ventral parts reflecting the field of view). The FWHM seems to be very large though. In general, it might be large due to (unusually) large applied or intrinsic smoothness, maybe 1) smoothing was applied accidentally another time / with a larger smoothing kernel (trivial) 2) the raw data were acquired with a (very) large voxel size, interpolation to 2x2x2 mm^3 would result in many more voxels, which are highly dependent though (might also be a scanner setting, some sequences offer to reconstruct the data with a higher spatial resolution than that with which it was acquired) 3) high spatial autocorrelation on single-subject level due to some global effects (massive drifts?) 4) possibly overfitted models, resulting in very small residuals (?) Thus, do you observe the FWHM for all your subjects (how much variability is there?), or only on the group level (which might be affected by a very extreme subject)? In the later case, is this just for a particular contrast / that particular one-sample t-test or for all the contrasts? Best Helmut